I just finished my speaker upgrade on my 2021 Prius Prime XLE, I ended up with the 12 speaker JBL configuration but may convert it back down to a 10 or 11 speaker with a 8" under seat powered sub. Using the factory 11.6" head unit from the XLE trim. I originally installed the JBL's on one side of the car first to observe the difference (Dash>RearDoor>FrontDoor). To be honest, the blend of half factory and half JBL created a more complete frequency range. SPEAKER UPGRADE: Dash 3.5": JBL Club 3520 (Installed the 270uf high pass capacitor or bass blocker) Front Door 6.5": JBL Club 620F Rear Door 6.5": JBL Club 6520 Sound Deadening: Killamat 80mil Front and Rear Doors XTC Baffle: 3.5" deep baffle for dash speaker to minimize bass cancellation against front speakers TBD Under seat powered sub: Rockville SS8P 8" (Check the amp panel against the JBL Nano or Infinity Basslink mini, its similar just inverted, could be from the same factory, also has similar bass controller) AFTER INSTALL RESULTS: -The JBL sounds brighter, higher highs, but lacks bass response (deeper boomy bass, but less than factory speakers and also lost punchier bass). -Factory Door speakers produced better bass response punchy and boomy (Natural Sounding Bass Drum) -The JBL Dash coaxial mid/tweeter created better voice production and highs on top, but the factory tweeter had better high hat sounds (Drum Cymbal). -When compared to the factory speakers, it sounds higher and brighter however, lower vocal ranges and bass range is not as complete. NUTSHELL RECOMMENDATION FOR IMPROVED SOUND BALANCE(HYBRID APPROACH): -Only replace the Dash and Rear Door speakers with the coaxial JBLs (or other coax brands) to bring out the mids and highs on those locations. -Keep the factory front door speaker to get better punchy and boomy bass response. -Sound Deadening DID NOT make any significant difference in sound, but knocking on the door makes it sound solid, not tinny anymore. Factory has a small square sound deadening patch on each door to remove major vibrations. -By having the coaxial JBL's on the Dash and Rear Door, it creates a wider spatial separation from front to rear while maintaining a more complete frequency range with the factory front door speakers. TIPS AND OBSERVATIONS: -When Toyota quotes 10 speakers, it means coaxial 2way speakers counts as two speakers. In the Prius/Prime there are only 6 speaker mounting enclosures/holes for all trims. -There was major sound Engineering involved from the factory systems to create a very balanced sound and tuned to the car's natural dynamics. True for both JBL and Non-JBL systems. I wouldn't doubt if Pioneer and Harman/JBL engineers were involved with the Toyota sound system designs. -Factory dash tweeter/speaker has 4 wires wired in parallel with the front door speaker. -Front dash speaker wire harness is compatible with many other Toyota dash speaker harness (eg. Tacoma, RAV4...) its the harness that has two wire loops to short the dash/front speakers. -XTC baffles will help minimize some bass cancelation from the back of the 3.5" speaker being out of phase with the front door speaker. Airspace behind the dash speakers blends with the driver/passenger front door speakers. -If the bass blocker eg. 270uf capacitor are not installed on the dash speakers, the mid vocal range can get over pronounced in the front. -Front sound is more pronounced than the rear, could be the parallel dash/front speakers to drop the impedance. -Dash Speakers are 3.5" drop ins, 2 - 10mm bolts. -Non-JBL 6 Toyota speaker system has the following, Dash: 2 Tweeters, Front Door: 2 Full Range, Rear Door: 2 Full Range, all 4 full range door speakers are the same part. -Use 11/64" drill bit to drill out the riveted speakers. -Use rivet nuts M6 or 1/4-20 in place of the rivet holes, need to open the holes up. Use a 9mm or 11/32" drill bit to widen the hole for the M6 or 14-20 rivet nut. -Without the rivet nut, you can find a self tapping screw that will grab the original rivet hole. -Others twist the speaker mounts a few degrees and screw a new self tapping hole, but I don't recommend this as you may not be dead center and the plastic on the door panel may rub into your woofer. -If you prefer to have all speaker locations to sound brighter, replace them all with coaxial speakers, but you may loose some spatial imaging from front to back. -Factory Door speakers have little to no highs, but has great bass response compared to the JBL's -Factory Dash tweeters produces better high hats, but lacks higher frequencies -Factory speakers are not junk, they cover a balanced sound, except for higher frequencies. -The JBL's distorted first on their bass performance compared to the factory door speaker. -I would get the speaker adapters and harness instead of destroying your factory door speakers to mount your coax upgrades. -The smaller magnets on the factory speakers are Neodymium thus stronger and lighter. Hope this helps you guys out! This should also apply to the 4th gen Prius.